Screw rotor machines for expanding a gaseous working medium of high temperature



March 7, 1967 T w H. R. NILSSON ET AL 3,307,453

SCREW ROTOR MACHINES FOR EXPANDING A GASEOUS WORKING MEDIUM 0? HIGH TEMPERATURE Filed Feb. 25, 1965 4 Sheets-*Sheet 1 I 33 W E INVENTORS ATTORNEY R. NILSSON ET AL March 7, 1967 SCREW ROTOR MACHINESIFOR EXPANDING A GASEOUS WORKING MEDIUM OF HIGH TEMPERATURE Filed Feb. 25;

4 Sheets-Sheet 2 Fig.2

gull/I INVENTORJ ATTORNE Y March 7, 1967 H. R.NILSSON ET AL 3,307,453 SCREW ROTOR MACHINES FOR EXPANDING A GASEOUS WORKING MEDIUM OF HIGH TEMPERATURE 4 Sheets-Sheet :5

Filed Feb. 25. 1965 I I I w ,5 7/ n w 74 I INVENTORY Wt fl ATTORNE Y March7, 1967 NILSSQN ET AL 3,307,453

SCREW ROTOR MACHINES FOR EXPANDING A GASEOUS 1 WORKING MEDIUM OF HIGH TEMPERATURE Filed Feb, 25, 1965 I i 4 Sheets-Sheet 4 INVENTUR) United States Patent Ofifice 3,307,453 Patented Mar. 7, 1967 3,307,453 SCREW RGTOR MACHINES FOR EXPANDING A GASEOUS WORKING MEDIUM OF HIGH TEM- PERATURE Hans Robert Niisson, Ektorp, and Lauritz Benedictus Schibbye, Saltsjo-Duvnas, Sweden, assignors to Svenska Rotor Maskiner Alktiebolag, Nacka, Sweden, a corporation of Sweden Filed Feb. 25, 1965, Ser. No. 435,160 Claims priority, application Sweden, Feb. 26, 1964, 2,320/64 13 Claims. ((31. 91-84) The present invention relates to a screw rotor machine for expanding a gaseous working medium of high temperature. This machine comprises a casing having a working space substantially consisting of two circular cylinders intersecting each other and having parallel axes and cooperating rotors sealingly enclosed by said cylinders. These rotors are provide-d with helical threads and troughs having a wrap angle less than 360. One rotor is of female rotor type, viz, it is so shaped that its threads and troughs are located at least in the main inside the pitch circle of the rotor and are provided with substantially concave flanks. The other rotor is of male rotor type, viz, it is so shaped that its threads and troughs are located at least in the main outside the pitch circle of the rotor and are provided with substantially convex flanks. The working space is provided with high pressure and low pressure ports located substantially on opposite sides of the plane through the axes of the cylinders. The high pressure port and the low pressure port are further connected with high pressure channels and low pressure channels, respectively, provided in the casing.

Machines of the type described have been previously suggested and tested but they have never resulted in any practical embodiment due to the thermal deformations of the casings and the rotors and altogether too great losses due to the cooling of the machine. These deformations have rendered it practically impossible in operation to utilize sufficiently high temperatures as well as to obtain such small clearances between the rotors and the casing and between the rotors themselves which are necessary for reaching an efficiency which in practice makes the machine capable of competing with other machines.

However, according to the present invention the difficulties arising from the thermal deformations are eliminated by a specific construction of the machine utilizing a material having an extremely low coefficient of thermal expansion amounting to only about 10% of that of steel. Such a material of ceramic type is now available which, besides, has sufficient mechanical strength at high temperatures and low heat conductivity as compared with steel and which further can be moulded and machined with great accuracy.

The invention will be described more in detail with reference to two embodiments illustrated in the accompanying drawings in which:

FIG. 1 is a longitudinal sectional view of a machine according to the invention taken on line 11 in FIG. 2,

FIG. 2 is a transverse section taken on line 22 in FIG. 1,

FIG. 3 is a longitudinal sectional view of another embodiment of a machine according to the invention taken on line 3-3 in FIG. 4, and

FIG. 4 is a transverse section taken on line 44 in FIG. 3.

The screw rotor machine shown in FIGS. 1 and 2 comprises a metallic casing 1t preferably of steel which casing has a low pressure end wall 12. The casing 10 and the end wall 12 are provided with channels 14 for a cooling fluid passing from an inlet opening 16 to an outlet opening 18. In the casing 10 there is a working space 20 having a lining 22 of a ceramic material having a very small coefiicient of thermal expansion and heat conductivity. The lining 22 is provided with projections 24 which support the lining within the casing 10 so that there are formed air-filled heat insulating spaces 26 between the casing 10 and the lining 22. The lining 22 is shaped such that the working space 20 therein substantially has the formof two circular cylinders intersecting each other. At the low pressure end wall 12 the lining 22 is provided with an opening corresponding to the form of the cylinders in which opening there is inserted a disk 28 of the same material as the lining 22. This disk 28 forms together with the lining 22 the walls of the working space 20. The disk 28 is fitted into the lining 22 and provided with projections 30 resting against the low pressure end wall 12 so that air-filled heat insulating-spaces 32 are formed also between the disk 28 and the low pressure end wall 12.

The casing 10 is also provided with a high pressure channel 34 having a lining 36 of the same material as the lining 22 or a similar material, gas-filled spaces 38 being formed between the casing 10 and the lining 36, A supply conduit 37 for the hot working fluid opens in said lining 36. The high pressure channel 34 communicates with the working space 20 through a high pressure port 40 in the lining 22. The casing 10 is further provided with a low pressure channel 42 lined by portions of the lining 22, said low pressure channel 42 communicating with the working space 20 through a low pressure port 44 in the lining 22. In order to restrict the heat transfer through the spaces 2d, 32 and 38 substantially due to heat radiation it is advisable to make the surfaces facing the spaces such that the radiation is reduced as far as possible. This can be done by choosing an appropriate material for the metallic surfaces so that the surfaces will be so light and shiny as possible and by applying an aluminium paint to the ceramic surfaces by means of painting or spray painting.

The high pressure port 46 is located partly in the high pressure end wall and partly in the barrel wall of the working space on one side of the plane containing the axes of the cylinders. The low pressure port 44 is located in the barrel wall of the working space 20 the main part lying on the side of the plane through the cylinder axes opposite to the high pressure port 40.

In the working space 20 there are two cooperating rotors, a female rotor 46 and a male rotor 48, and the axes of these rotors substantially coincide with the cylinder axes. These rotors are journalled in the casing 10 at the high pressure end of the working space in cylinder roller bearings 50 and in the low pressure end wall 12 in matched ball bearings 52 with shoulders. The female rotor 46 consists of a tubular metallic central body 54 forming axle journals for the rotor and an outer body 56 of the same material as the lining 22 or a similar material. The central body and the outer body are non-rotatably connected to each other by means of a pin 58 passing radially through the rotor and also preventing axial relative movement. The outer body 56 is provided with internal supporting projections 57 cooperating with the central body 54, and between these projections are formed air-filled heat insultating spaces 59. On its outer side the outer body is provided with six helical threads 60 with a wrap angle of about 173. The threads 60 lie in the main inside the pitch circle of the rotor and the flanks are substantially concave, the troughs 62 between the threads 60 having, when seen in a transverse plane, a cross section shaped approximately as a segment of a circle. In a corresponding manner the male rotor 48 consists of a tubular metallic central body 64 and an outer body 66 of the same material as the lining 22 or of a similar material. A torsion bar 68 projects into the central body 64 and is provided with a close-fitting end portion having axial channels 70. The outer body 66, the central body 64 and the torsion bar 68 are non-rotatably connected to each other by means of a pin 72 passing radially through the rotor and also preventing axial relative movement. The outer body 66 has internal supporting projections 73 cooperating with the central body 64, and between these projections there are airfilled heat insulating spaces 77. On its outer side the rotor is provided with four helical threads '74 and intervening troughs 76 having a 'wrap angle of about 260. The threads 74 lie in the main outside the pitch circle of the rotor and the flanks are substantially convex, the form of the flanks being such that there is a continuous sealing line between the rotors 46 and 48. Further, the rotors 4-6 and 43 are rotationally coupled to each other by means of a synchronizing mechanism 78 of the gear Wheel type located adjacent to the bearings 52. The central bodies 54 and 64 of the rotors 46 and 46, respectively, are sealed against the casing and the low pressure end wall by means of sealing elements 80 and 82, respectively. For supplying a cooling fluid to the inside of the central bodies 54 and 64 of the rotors 46 and 48, respectively, and for discharging said fluid there is provided in the casing 16 and in the low pressure end wall 12 a stationary inlet 84 and a stationary outlet 86 for the cooling fluid, said inlet and outlet being sealingly connected with the ends of the central bodies 54, 64. The torsion bar 68 passes through an opening in the cooling fluid inlet 64 and forms the output shaft of the machine.

The cooling fluid may consist of a circulating liquid or a gas, preferably air, which after having passed the cooling passages of the machine is heated in a combustion chamber and utilized as working fluid in the machine. Owing to the thermal deformations it is desirable to keep the whole casing at so uniform a temperature as possible and it is therefore advantageous to use a cooling fluid which absorbs heat by evaporation of a liquid medium. Moist steam, for instance, is such a cooling fluid.

The machine operates as follows. Working fluid of high temperature enters through a supply conduit 37 and a high pressure channel 34 into the high pressure port 41?, the casing 10 being protected from the high temperature by the lining 36 and the spaces 38. The working fluid flows from the high pressure port into the portions of the rotor troughs 62 and '76 communicating therewith. Hereby the rotors 46 and 48 are subjected to a torque which rotates the rotors such that said trough portions increase in volume. The rotor threads and 7 4 lying behind the troughs 62 and 76, respectively, when seen in the direction of rotation, then pass the edges of the high pressure port so that there is formed a V-shaped expansion chamber separated from the high pressure and low pressure ports 40 and 44. The volume of the V-shaped chamber increases continuously during the rotation of the rotors until its volume amounts to the sum of the full volumes of the two communicating troughs 62 and 76 and thereafter the troughs are opened towards the low pressure port and the expanded working fluid is discharged from the machine through the low pressure channel 42.

In the machine shown in FIGS. 3 and 4 the casing comprises three elements, viz. a middle barrel section 110, a high pressure end wall 112 and a low pressure end wall 114, all three elements being made for instance from cast steel. The elements are provided with passages 116 for a cooling fluid which is supplied to and discharged from the elements through conduits 118 and 120 respectively.

The middle casing section 110 and the high pressure end wall 112 form together a high pressure or inlet channel 122 while a low pressure or outlet channel 124 is located entirely in the middle casing section 110.

All surfaces of the steel casing which are exposed to the hot working medium are covered by a layer 126 of ceramic material which in this case is applied by flame spraying. This ceramic material has a very low coefficient of thermal expansion and a very low heat conductivity and therefore the ceramic layers do not themselves undergo any appreciable deformation when heated and due to the excellent heat'insulating properties of the ceramic material the surrounding metallic casing structure may be held at such a low temperature that its thermal deformation will be tolerable.

The hot working medium is supplied through a conduit 128 in which is inserted a lining in the form of a sheet metal tube 131) the inside of which is coated by ceramic material. A corresponding lining 132 is inserted in the high pressure channel 122. Cooling air is conveyed through the annular space between the tube and the conduit 128 and this air flows on both sides of the lining 132 in the high pressure channel 122 in order to reduce the heating of the casing at this point where the temperature of the working medium has its highest value.

In this embodiment both rotor bodies 134 and 136 are made entirely from ceramic material. As shown in FIG. 3 the male rotor body 134 is provided at its low pressure end with a stud 138 which projects into an opening in the low pressure end wall 114 where it is rigidly connected to a metallic tubular shaft 140. The end of this shaft 140 is shrunk on the stud 138 and secured in a fixed angular relationship to the stud by means of pins 142 or the like. The shaft 140 is joumaled in a slide bearing 144 and matched ball bearings 146 with shoulders which bearings are provided in a housing 148 secured to the low pressure end wall 114.

The low pressure end of the female rotor body 136 is supported in exactly the same manner and outside the bearings 144 and 146 the two rotor shafts carry gear wheels forming a synchronizing gear 150. Numeral 152 indicates a nozzle for supplying lubricating oil to said gear.

As shown in FIG. 3 the inner end of the shaft 140 cooperates with a bushing 154 to form a labyrinth seal to which blocking air is supplied from a conduit 156. This blocking air exerts a cooling action on the shaft 140 which is further cooled by lubricating oil supplied to the slide bearing 144 through a conduit 153. Numeral indicates an oil outlet from the housing 148.

A corresponding labyrinth seal is provided also for the female rotor shaft.

The high pressure end of the rotor body 134 is hollow the outer portion of the cavity being in the form of a cylindrical bore and the inner portion being of square cross section. In the cylindrical bore is inserted a bushing 162 by means of which the high pressure end of the rotor body is journaled on a stationary hollow stub shaft 164 carried by the low pressure end wall 112 and projecting into the rotor cavity. Lubricating oil is supplied to the bearing through a bore 166 in the stub shaft 164. This lubricating oil exerts a cooling action upon the rotor body end as well as upon the stub shaft.

The high pressure end of the rotor body 134 is further provided with an axially directed collar 168- cooperating with a bushing 170 to form a labyrinth seal to which blocking air is supplied through a conduit 172.

In the inner square portion of the rotor body cavity is inserted a correspondingly shaped bushing 174 which is provided with intern-a1 splines. A shaft 176 having a head 178 with corresponding external splines extends from said bushing 174 through the hollow stub shaft 164 to the outside of the machine and forms the output shaft of the same.

The lubricating oil supplied to the bearing inside the rotor body is drained off through a conduit 180.

The arrangement at the high pressure end of the female rotor body 136 is the same as that now described with reference to the high pressure end of the male rotor body 134 with the exception that there is no torque transmitting shaft corresponding to the shaft 176 and therefore there is no need of a cavity portion of non circular cross section inside the cylindrical bore containing the bearing bushing 162.

The expansion of the working fluid takes place substantially in a closed chamber of continuously increasing volume which, as is well known, isa condition precedent for a high expansion efficiency in a machine of the displacement 'type. The expansion chambers are in their entirety lined with a material having a great resistingpower at high temperatures and a small coefficient of thermal expansion. Therefore, the working fluid can be supplied at a very high temperature of between l000 and 2000 C., and preferably at a temperature of 1500' to 1600" C., which is of greatest importance for obtaining a high thermal efiiciency. Owing to the fact that the said mate-rial has a low heat conductivity it is possible to restrict the heat quantity which is removed from the working fluid through the casing and the rotors by cool ing. This reduces the cooling losses which involves a further increase of the efficiency of the machine. The quantity of cooling fluid passing through the casing and the rotors may preferably be adjusted such that the temperature distribution in the different parts will be substantially uniform so that the thermal expansion cannot cause any harmful warping. As a result of this measure the machine can operate with very small clearances in spite of the high temperature which involves small leakage losses further contributing to a high expansion efliciency.

From the foregoing it 'will be evident that for the purposes ofthe present invention, the two most important characteristics of ceramic materials suitable for carrying the invention into practice are dimensional stability over a wide temperature range, by virtue of a very low coeificient of thermal expansion, and/ or a very low coefficient of thermal conductivity over such a temperature range. Such materials are known and are commercially available and materials having the properties of great thermal stability with low heat conductivity as well are products of the Corning Glass Works, Corning, New York, manufactured in accordance with the disclosure of US. Patents No. 2,920,971, dated January 12, 1960, and/or No. 3,096,159 dated July 2, 1963, such products in certain forms being marketed under the trade name Cercor and physical properties thereof important to the present invention being given, not only in the aforementioned patents but also in the Corning Companys bulletin NPC 4 entitled Cercor Glass Ceramic Structures. A material considered to be suitable for the purposes of the present invention is that designated as Code 9690 in the aforesaid bulletin.

For those embodiments of the invention in which elements exposed to high temperature are ceramic coated by flame spraying, stabilized metallic oxides, particularly zirconia, produced by the Norton Company of Worcester, Mass, and of which the products disclosed in US. Patent Nos. 2,535,526 dated December 26, 1960, and 2,876,121, dated March 3, 1959, are examples, are suitable materials, which are applicable by means of flame spraying in ac, cordance with the disclosure in US. Patent No. 2,707,691, dated May 3, 1955.

While for purposes of illustration and by way of example only, certain embodiments of structure are shown suitable for carrying the present invention into effect, it

6 will be understood that many different modifications and combinations of elements may be employed to meet different specification and operating conditions. Thus, for example, cooled rotors of the kind disclosed in the embodiment of FIG. 1 may be employed with a coated casing structure of the kind shown in the embodiment of FIG. 3 and similarly, rotors of the ceramic coated metal body type may be employed with either type of casing. Accordingly it is to be understood that all forms of structure falling within the terms of the appended claims are embraced within the scope of the present invention.

What we claim is:

1. ln screw rotor machine apparatus of the character described for expanding a high temperature gaseous medium and having a metallic casing with a working space therein consisting of two intersecting bores, an end wall at each end thereof, an inlet and an outlet, a male rotor rotatably mounted in one of said bores and a female rotor in the other said bore with said rotors meshing with each other, the combination which comprises ceramic material disposed on all the surfaces of said working space, said end walls and said rotors which are exposed to said high temperature working medium, with said ceramic material having a coefficient of thermal expansion of less than 3 x 10, synchronizing gear means for interconnecting said male and said female rotors outside said working space, and cooling means in said metallic casing for cooling the metallic portions thereof which have disposed thereon said ceramic material.

2. Apparatus as described in claim 1 in which each rotor has a central metallic core and said ceramic material disposed on the surfaces thereof is in the form of a ceramic body surrounding said core, and means for cooling said metallic core.

3. Apparatus as described in claim 1 in which said rotors are metallic and the ceramic material disposed on the surface thereof is applied by flame spraying.

4. Apparatus as described in claim 1 in which said rotors are substantially entirely of said ceramic material.

5. Apparatus as described in claim 4 which includes a stud shaft disposed in one end of each of said rotors and extending through the adjacent said end wall, a metallic shaft connected to and extending into each of said stud shafts with said metallic shafts being connected to said synchronizing gear means, and means for cooling each of said metallic shafts.

6. Apparatus as described in claim 5 in which each of said stud shafts has disposed thereon one portion of a labyrinth seal at the point where said shafts extend through said end wall, with means connected to said wall for supplying blocking air thereto.

7. Apparatus as described in claim 4 in which each of said rotors has at one end thereof a cavity with a metallic bearing bushing disposed therein, and in which a stationary stud shaft extends into each of said bushings for supporting the adjacent end of said rotors.

8. Apparatus as described in claim 7 in which the cavity of the said male rotor inside said bushing is noncircular in cross section, with the stud shaft being hollow, and in which the output shaft of said rotor is non-rotatably disposed in said non-circular cross section and extends through said hollow stud shaft to the outside of said machine.

9. Apparatus as described in claim 6 in which an axially directed collar is disposed upon and surrounds said stud shaft, and forms one element of said labyrinth seal.

10. Apparatus as described in claim 1 in which said ceramic material consists of a separate internal ceramic lining element for lining said metallic casing and said end walls and is supported thereby.

11. Apparatus as described in claim 1 in which said ceramic material consists of coating on said metallic material applied by flame spraying.

7 8 13. Apparatus as described in claim 1 in which said 2,873,909, 2/1959 Nilsson 230-143 ceramic material has a coefficient of thermal expansion 3,128,710 4/1964 Blomgren et a1 103-426 of 1.5 X 10- or less. 3,129,877 4/1964 Nilsson et al 230-143 References Cited by the Examiner 5 v 802 3 0 2 FOREISN PATENTS UNITED STATES PATENTS 1 1951 ermany' 1 7 934 2 1 77 Temple 103 216 DQNLEY J- STOCKING, Primary Examiner.

2,799,253 7/1957 Lindhagen et a1 230143 WILBUR J. GOODLIN, Examiner. 

1. IN SCREW ROTOR MACHINE APPARATUS OF THE CHARACTER DESCRIBED FOR EXPANDING A HIGH TEMPERATURE GASEOUS MEDIUM AND HAVING A METALLIC CASING WITH A WORKING SPACE THEREIN CONSISTING OF TWO INTERSECTING BORES, AND END WALL AT EACH END THEREOF, AN INLET AND AN OUTLET, A MALE ROTOR ROTATABLY MOUNTED IN ONE OF SAID BORES AND A FEMALE ROTOR IN THE OTHER SAID BORE WITH SAID ROTORS MESHING WITH EACH OTHER, THE COMBINATION WHICH COMPRISES CERAMIC MATERIAL DISPOSED ON ALL THE SURFACES OF SAID WORKING SPACE, SAID END WALLS AND SAID ROTORS WHICH ARE EXPOSED TO SAID HIGH TEMPERATURE WORKING MEDIUM, WITH SAID CERAMIC MATERIAL HAVING A COEFFICIENT OF THERMAL EXPANSION OF LESS THAN 3 X 10-6, SYNCHRONIZING GEAR MEANS FOR INTERCONNECTING SAID MALE AND SAID FEMALE ROTORS OUTSIDE SAID WORKING SPACE, AND COOLING MEANS IN SAID METALLIC CASING FOR COOL- 